The disposal of municipal and industrial waste products is an extremely important issue that is receiving a great deal of attention. The problem of waste disposal involves not only the development of adequate techniques and means for handling these wastes, but also the correction of serious problems that have been created due to past improper and unsafe practices. Serious contamination of the environment has resulted from the lack of knowledge of, or lack of desire to implement, effective methods for the disposal, storage, and containment of these undesirable waste products. The problem is magnified many fold by the great number of disposal sites existing today and the large size of these sites.
In situations in which on-line or in-situ processing is either not technically feasible or overly cost prohibitive, attempts have been made to contain the wastes by creating isolation covers for the waste piles. Although this course of action has been pursued at many waste sites, all too often these isolation covers fail to prevent the escape of contaminants.
In an effort to develop more effective covers for waste areas, the unique characteristics of water-swellable clays have been used extensively. The mineral sodium montmorillonite, generally known as sodium bentonite, is one such clay. As reported in the publication Science, Feb. 23, 1996, S. Karaborni, et al. write, "Clays have a characteristic layered structure. Between these layers, water can absorb, resulting in strong repulsive forces that cause the clays to expand to as much as several times their original thickness. Clay hydration studies have been conducted since 1933, yet there is no clear understanding of the swelling mechanism." Nevertheless, water-swelling clays have been used by the industry in a number of products and in a variety of applications.
In soil sealing applications, bentonite clays have been mixed with other ingredients in both wet and dry conditions. For instance, in U.S. Pat. No. 3,016,713, issued to Deming, a method for treating soil surfaces with an aqueous slurry of a lattice clay (bentonite) and an additive of a water-soluble anionic polyelectrolyte is described as rendering the walls and bottoms of stock ponds and other water reservoirs impervious to seepage or other leaking. U.S. Pat. No. 3,986,365, issued to Hughes, teaches a soil sealing method in which an amount of a particular water-soluble polymer is added to a dry bentonite-soil admixture whereby the polymer addition decreases the amount of bentonite necessary to form a water-containing soil enclosure. U.S. Pat. No. 3,772,893, issued to Eilers, teaches a soil sealing method used to reduce the permeability of soil solids to water by admixing a dry mixture of an expanding lattice clay and a linear water soluble organic polymer to a layer of soil. The soil layer is then compacted using ASTM D 698-91 procedures.
Bentonite clays have also been used as water barrier elements in geosynthetic fabric liners. These liners typically consist of a layer of dry bentonite clay sandwiched between two non-woven geotextile fabrics. This technology is described in U.S. Pat. No. 5,346,566, issued to White, and U.S. Pat. No. 5,112,665, issued to Alexander. Geosynthetic clay liners of this type are being used in landfill covers as water barriers to eliminate the need of a compacted clay layer. Although these liners, when compared with compacted clay, have low hydraulic conductivity specifications and are usually cost competitive, seam integrity can be a problem and installation costs can be excessive.
The use of compacted clay covers has been a traditional method of complying with the requirements of the U.S. Environmental Protection Agency. Normally, a three layer system is used for the formation of such covers. In such systems, a top vegetative layer, an intermediate drainage layer, and a clay bottom layer are used. The bottom layer is typically a compacted clay that comprises native soil mixed with dry bentonite clay in a concentration of at least 5% by weight. Although compaction of this layer to a point slightly wet of optimum initially achieves adequate hydraulic conductivity, conventional clay covers have been shown to be vulnerable to desiccation cracking, especially when they are installed in arid environments. Such cracking drastically reduces the effectiveness of the cover and can even result in total cover failure. In addition to having such cracking problems, compacted clay covers of this type are usually expensive and difficult to construct.
Because of the inadequacies of current state-of-the-art environmental protection measures, various governmental agencies are actively engaged in programs directed toward the improvement of environmental restoration and management technologies. Accordingly, it can be appreciated that it would be desirable to have a waste containment system which effectively prevents contamination of the surrounding environment that is neither vulnerable to failure nor cost prohibitive.